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In the cold dark matter cosmology, the baryonic components of galaxies—stars and gas—are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius—a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

Aims. An unbiased and detailed characterization of the galaxy luminosity function (LF) is a basic requirement in many astrophysical issues: it is of particular interest in assessing the role of the environment in the evolution of the LF of different galaxy types.

Aims. We study the dependence of galaxy clustering on luminosity and stellar mass at redshifts $z\sim$[0.2–1], using the first 10K redshifts from the zCOSMOS spectroscopic survey of the COSMOS field.

Context. For more than two decades we have known that galaxy morphological segregation is present in the Local Universe. It is important to see how this relation evolves with cosmic time.

Aims. We investigate the relationships between three main optical galaxy observables (spectral properties, colors, and morphology), exploiting the data set provided by the COSMOS/zCOSMOS survey. The purpose of this paper is to define a simple galaxy classification cube, with a carefully selected sample of ≈1000 galaxies.

We have undertaken an HST Space Telescope Imaging Spectrograph survey of 54 late type spiral galaxies to study the scaling relations between black holes and their host spheroids at the low mass end. Our aim is to measure black hole masses or to set upper limits for a sizeable sample of spiral galaxies. In this paper we present new Space Telescope Imaging Spectrograph (STIS) observations of three spiral galaxies, NGC 4303, NGC 3310 and NGC 4258. The bright optical emission lines Hαλ$6564~\AA$, [NII] λλ$6549,6585~\AA$and [SII] λλ$ 6718,6732~\AA$were used to study the kinematics of the ionized gas in the nuclear region of each galaxy with a ~$0.07\arcsec$spatial resolution. Our STIS data for NGC 4258 were analyzed in conjunction with archival ones to compare the gas kinematical estimate of the black hole mass with the accurate value from H2O-maser observations.
In NGC 3310, the observed gas kinematics is well matched by a circularly rotating disk model but we are only able to set an upper limit to the BH mass which, taking into account the allowed disk inclinations, varies in the range $5.0 \times 10^{6}$–$\,4.2 \times 10^{7}~M_{\odot}$at the 95% confidence level. 
In NGC 4303 the kinematical data require the presence of a BH with mass $M_{\rm BH}=(5.0)^{+0.87}_{-2.26}\times 10^{6}~M_{\odot}$(for a disk inclination $i=70$deg) but the weak agreement between data and disk model does not allow us to consider this measurement completely reliable. If the allowed inclination values are taken into account, MBHvaries in the range $6.0 \times 10^{5}$–$1.6 \times 10^{7}~M_{\odot}$at the 95% confidence level.
In NGC 4258, the observed kinematics require the presence of a black hole with $M_{\rm BH}= (7.9)^{+6.2}_{-3.5} \times 10^{7}~M_{\odot}$($i=60$deg) and, taking into account reasonable limits for the inclination, MBHis in the range $2.5\times 10^{7}$–$2.6 \times 10^{8}~M_{\odot}$at the 95% confidence level. This result is in good agreement with the published value $(3.9 \pm 0.1) \times 10^{7}~M_{\odot}$, derived from H2O-maser observations. As in the case of NGC 4303, the agreement between observed and model kinematics is not strong but this does not affect the recovery of the correct MBHvalue. 
Our attempt at measuring BH masses in these 3 late type Sbc spiral galaxies has shown that these measurements are very challenging and at the limit of the highest spatial resolution currently available. Nonetheless our estimates are in good agreement with the scaling relations between black holes and their host spheroids suggesting that (i) they are reliable and (ii) black holes in spiral galaxies follow the same scaling relations as those in more massive early-type galaxies. A crucial test for the gas kinematical method, the correct recovery of the known BH mass in NGC 4258, has been successful.

Aims.Our goal is to develop a new and reliable statistical method to classify galaxies from large surveys. We probe the reliability of the method by comparing it with a three-dimensional classification cube, using the same set of spectral, photometric and morphological parameters.

We study the impact of the environment on the evolution of galaxies in the zCOSMOS 10 k sample in the redshift range 0.1 ≤ z≤ 1.0 over an area of  ~1.5 deg2. The considered sample of secure spectroscopic redshifts contains about 8500 galaxies, with their stellar masses estimated by SED fitting of the multiwavelength optical to near-infrared (NIR) photometry. The evolution of the galaxy stellar mass function (GSMF) in high and low density regions provides a tool to study the mass assembly evolution in different environments; moreover, the contributions to the GSMF from different galaxy types, as defined by their SEDs and their morphologies, can be quantified. At redshift z~ 1, the GSMF is only slightly dependent on environment, but at lower redshifts the shapes of the GSMFs in high- and low-density environments become extremely different, with high density regions exhibiting a marked bimodality, not reproducible by a single Schechter function. As a result of this analysis, we infer that galaxy evolution depends on both the stellar mass and the environment, the latter setting the probability of a galaxy to have a given mass: all the galaxy properties related to the stellar mass show a dependence on environment, reflecting the difference observed in the mass functions. The shapes of the GSMFs of early- and late-type galaxies are almost identical for the extremes of the density contrast we consider, ranging from isolated galaxies to rich group members. The evolution toward z= 0 of the transition mass ℳcross, i.e., the mass at which the early- and late-type GSMFs match each other, is more rapid in high density environments, because of a difference in the evolution of the normalisation of GSMFs compared to the total one in the considered environment. The same result is found by studying the relative contributions of different galaxy types, implying that there is a more rapid evolution in overdense regions, in particular for intermediate stellar masses. The rate of evolution is different for sets of galaxy types divided on the basis of their SEDs or their morphologies, tentatively suggesting that the migration from the blue cloud to the red sequence occurs on a shorter timescale than the transformation from disc-like morphologies to ellipticals. Our analysis suggests that environmental mechanisms of galaxy transformation start to be more effective at z< 1. The comparison of the observed GSMFs to the same quantities derived from a set of mock catalogues based on semi-analytical models shows disagreement, in both low and high density environments: in particular, blue galaxies in sparse environments are overproduced in the semi-analytical models at intermediate and high masses, because of a deficit of star formation suppression, while at z< 0.5 an excess of red galaxies is present in dense environments at intermediate and low masses, because of the overquenching of satellites.

Aims.With the first  ~10 000 spectra of the flux limited zCOSMOS sample (IAB≤ 22.5) we want to study the evolution of environmental effects on galaxy properties since z~ 1.0, and to disentangle the dependence among galaxy colour, stellar mass and local density.

Aims. We investigate the properties and the environment of radio sources with optical counterparts from the combined VLA-COSMOS and zCOSMOS samples. The advantage of this sample is the availability of optical spectroscopic informations, high quality redshifts, and accurate density determination.Methods. By comparing the star formation rates estimated from the optical spectral energy distribution with those based on the radio luminosity, we divide the radio sources in to three families passive AGN, non-passive AGN, and star-forming galaxies. These families occupy specific regions of the 8.0-4.5 µm infrared color- specific star-formation plane, from which we extract the corresponding control samples.Results. Only the passive AGN have a significantly different environmental distribution from their control sample. The fraction of radio-loud passive AGN increases from ~2% in underdense regions to ~15% for overdensities (1 + d) greater than 10. This trend is also present as a function of richness of the groups hosting the radio sources. Passive AGN in overdensities tend to have higher radio luminosities than those in lower density environments. Since the black hole mass distribution is similar in both environments, we speculate that, for low radio luminosities, the radio emission is controlled (by fuel availability or confinement of the radio jet by local gas pressure) by the interstellar medium of the host galaxy, while in other cases it is determined by the structure (group or cluster) in which the galaxy resides.

Aims. We investigate the properties and the environment of radio sources with optical counterparts from the combined VLA-COSMOS and zCOSMOS samples. The advantage of this sample is the availability of optical spectroscopic informations, high quality redshifts, and accurate density determination.

Aims. We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The selected sample covers a wide redshift range (0.15 < z< 0.92) and is deeper than any other previous study, encompassing the luminosity range $10^{5.5}$$L_{\odot}$< $L_{\rm [OIII]}$< $10^{9.1}$$L_{\odot}$. We explore the intrinsic properties of these AGN and the relation to their X-ray emission (derived from the XMM-COSMOS observations). We study their evolution by computing the [O iii]λ5007$~\AA$line luminosity function (LF) and we constrain the fraction of obscured AGN as a function of luminosity and redshift.

Aims. We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The selected sample covers a wide redshift range (0.15 < z< 0.92) and is deeper than any other previous study, encompassing the luminosity range 105.5$L_{\odot}$< $L_{\rm [OIII]}$< 109.1$L_{\odot}$. We explore the intrinsic properties of these AGN and the relation to their X-ray emission (derived from the XMM-COSMOS observations). We study their evolution by computing the [O?iii]?5007 Å line luminosity function (LF) and we constrain the fraction of obscured AGN as a function of luminosity and redshift.Methods. The sample was selected on the basis of the optical emission line ratios, after applying a cut to the signal-to-noise ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams ([O?iii]/Hß versus [N?ii]/Ha and [O?iii]/Hß versus [S?ii]/Ha) to isolate AGN in the redshift range 0.15 < z< 0.45 and the diagnostic diagram [O?iii]/Hß versus [O?ii]/Hß to extend the selection to higher redshift (0.5 < z< 0.92).Results. Combining our sample with one drawn from SDSS, we found that the best description of the evolution of type-2 AGN is a luminosity-dependent density evolution model. Moreover, using the type-1 AGN LF we were able to constrain the fraction of type-2 AGN to the total (type-1?+?type-2) AGN population. We found that the type-2 fraction decreases with luminosity, in agreement with the most recent results, and shows signs of a slight increase with redshift. However, the trend with luminosity is visible only after combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the type-2 fraction seems to be quite constant with luminosity.

Aims. The identities of the main processes triggering and quenching star-formation in galaxies remain unclear. A key stage in evolution, however, appears to be represented by post-starburst galaxies. To investigate the prevalence of these galaxies and their impact on galaxy evolution in general, we initiated a multiwavelength study of galaxies with k+aspectral features in the well-studied COSMOS field.Methods. We examine a mass-selected sample of k+agalaxies in the COSMOS field at z= 0.48-1.2 using the spectroscopic zCOSMOS sample. To classify galaxies in their k+aphase, we use a spectroscopic criterion, based on the amplitude of the Hdabsorption line and the absence of the [OII] emission line. We develop our analysis for a well-defined sample by imposing stringent confidence levels on the spectroscopic redshifts and spectral measurements. We compare our results for two mass-selected samples of star-forming and quiescent galaxies selected using a purely spectral classification scheme from the 10?000 zCOSMOS catalogue (i.e.?, based on measurements of 4000 Å break and EW[OII]).Results. In our mass-limited sample, k+agalaxies occupy the brightest tail of the luminosity distribution. They are as massive as quiescent galaxies and populate the green valley in the colour versus luminosity (or stellar mass) distribution. A small percentage (<8%) of these galaxies have radio and/or X-ray counterparts (implying an upper limit to the SFR of ~8  $\cal M_\odot$?yr-1). Over the entire redshift range explored, the class of post-starburst galaxies is morphologically a heterogeneous population with a similar incidence of bulge-dominated and disky galaxies. This distribution does not vary with the strength of the Hdabsorption line but instead with stellar mass in a way reminiscent of the well-known mass-morphology relation. The results about the incidence of asymmetries and the concentration of the light distribution derived from HST/ACS images imply that this galaxy population possibly represents an intermediate stage of galaxy evolution. Although k+agalaxies are also found in underdense regions, they appear to reside typically in a similarly rich environment as quiescent galaxies on a physical scale of ~2–8 Mpc, and in groups they show a morphological early-to-late type ratio similar to the quiescent galaxy class. With the current data set, we do not find evidence of statistical significant evolution in either the number/mass density of k+agalaxies at intermediate redshift with respect to the local values, or the spectral properties, although more solid results on this and other aspects will be obtained following the completion of the survey.Conclusions. Several mechanisms related and unrelated to the environment are at work in quenching star-formation activity in galaxies on short timescales (<1 Gyr). Those galaxies, which are affected by a sudden quenching of their star-formation activity, may increase the stellar mass of the red-sequence by up to a non-negligible level of ~10%.

Context. Groups of galaxies are a common environment, bridging the gap between starforming field galaxies and quiescent cluster galaxies. Within groups secular processes could be at play, contributing to the observed strong decrease of star formation with cosmic time in the global galaxy population.Aims. We took advantage of the wealth of information provided by the first ~10?000 galaxies of the zCOSMOS-bright survey and its group catalogue to study in detail the complex interplay between group environment and galaxy properties. Methods. The classical indicator $F_{\rm blue}$, i.e., the fraction of blue galaxies, proved to be a simple but powerful diagnostic tool. We studied its variation for different luminosity and mass selected galaxy samples, divided as to define groups/field/isolated galaxy subsamples.Results. Using rest-frame evolving B-band volume-limited samples, the groups galaxy population exhibits significant blueing as redshift increases, but maintains a systematic difference (a lower $F_{\rm blue}$) with respect to the global galaxy population, and an even larger difference with respect to the isolated galaxy population. However moving to mass selected samples it becomes apparent that such differences are largely due to the biased view imposed by the B-band luminosity selection, being driven by the population of lower mass, bright blue galaxies for which we miss the redder, equally low mass, counterparts. By carefully focusing the analysis on narrow mass bins such that mass segregation becomes negligible we find that only for the lowest mass bin explored, i.e., $\log ({\cal M}_{*}/{\cal M}_{\odot}) \leq 10.6 $, does a significant residual difference in color remain as a function of environment, while this difference becomes negligible toward higher masses.Conclusions. Our results indicate that red galaxies of mass $\log ({\cal M}_{*}/{\cal M}_{\odot}) \geq 10.8$are already in place at z~ 1 and do not exhibit any strong environmental dependence, possibly originating from so-called nature or internal mechanisms. In contrast, for lower galaxy masses and redshifts lower than z~ 1, we observe the emergence in groups of a population of nurture red galaxies: slightly deviating from the trend of the downsizing scenario followed by the global galaxy population, and more so with cosmic time. These galaxies exhibit signatures of group-related secular physical mechanisms directly influencing galaxy evolution. Our analysis implies that these mechanisms begin to significantly influence galaxy evolution after z~ 1, a redshift corresponding to the emergence of structures in which these mechanisms take place.

Aims. The identities of the main processes triggering and quenching star-formation in galaxies remain unclear. A key stage in evolution, however, appears to be represented by post-starburst galaxies. To investigate the prevalence of these galaxies and their impact on galaxy evolution in general, we initiated a multiwavelength study of galaxies with k+aspectral features in the well-studied COSMOS field.Methods. We examine a mass-selected sample of k+agalaxies in the COSMOS field at z= 0.48-1.2 using the spectroscopic zCOSMOS sample. To classify galaxies in their k+aphase, we use a spectroscopic criterion, based on the amplitude of the Hdabsorption line and the absence of the [OII] emission line. We develop our analysis for a well-defined sample by imposing stringent confidence levels on the spectroscopic redshifts and spectral measurements. We compare our results for two mass-selected samples of star-forming and quiescent galaxies selected using a purely spectral classification scheme from the 10?000 zCOSMOS catalogue (i.e.?, based on measurements of 4000 Å break and EW[OII]).Results. In our mass-limited sample, k+agalaxies occupy the brightest tail of the luminosity distribution. They are as massive as quiescent galaxies and populate the green valley in the colour versus luminosity (or stellar mass) distribution. A small percentage (<8%) of these galaxies have radio and/or X-ray counterparts (implying an upper limit to the SFR of ~8  $\cal M_\odot$?yr-1). Over the entire redshift range explored, the class of post-starburst galaxies is morphologically a heterogeneous population with a similar incidence of bulge-dominated and disky galaxies. This distribution does not vary with the strength of the Hdabsorption line but instead with stellar mass in a way reminiscent of the well-known mass-morphology relation. The results about the incidence of asymmetries and the concentration of the light distribution derived from HST/ACS images imply that this galaxy population possibly represents an intermediate stage of galaxy evolution. Although k+agalaxies are also found in underdense regions, they appear to reside typically in a similarly rich environment as quiescent galaxies on a physical scale of ~2–8 Mpc, and in groups they show a morphological early-to-late type ratio similar to the quiescent galaxy class. With the current data set, we do not find evidence of statistical significant evolution in either the number/mass density of k+agalaxies at intermediate redshift with respect to the local values, or the spectral properties, although more solid results on this and other aspects will be obtained following the completion of the survey.Conclusions. Several mechanisms related and unrelated to the environment are at work in quenching star-formation activity in galaxies on short timescales (<1 Gyr). Those galaxies, which are affected by a sudden quenching of their star-formation activity, may increase the stellar mass of the red-sequence by up to a non-negligible level of ~10%.

Context. Groups of galaxies are a common environment, bridging the gap between starforming field galaxies and quiescent cluster galaxies. Within groups secular processes could be at play, contributing to the observed strong decrease of star formation with cosmic time in the global galaxy population.Aims. We took advantage of the wealth of information provided by the first ~10?000 galaxies of the zCOSMOS-bright survey and its group catalogue to study in detail the complex interplay between group environment and galaxy properties. Methods. The classical indicator Fblue, i.e., the fraction of blue galaxies, proved to be a simple but powerful diagnostic tool. We studied its variation for different luminosity and mass selected galaxy samples, divided as to define groups/field/isolated galaxy subsamples.Results. Using rest-frame evolving B-band volume-limited samples, the groups galaxy population exhibits significant blueing as redshift increases, but maintains a systematic difference (a lower Fblue) with respect to the global galaxy population, and an even larger difference with respect to the isolated galaxy population. However moving to mass selected samples it becomes apparent that such differences are largely due to the biased view imposed by the B-band luminosity selection, being driven by the population of lower mass, bright blue galaxies for which we miss the redder, equally low mass, counterparts. By carefully focusing the analysis on narrow mass bins such that mass segregation becomes negligible we find that only for the lowest mass bin explored, i.e., $\log ({\cal M}_{*}/{\cal M}_{\odot}) \leq 10.6 $, does a significant residual difference in color remain as a function of environment, while this difference becomes negligible toward higher masses.Conclusions. Our results indicate that red galaxies of mass $\log ({\cal M}_{*}/{\cal M}_{\odot}) \geq 10.8$are already in place at z~ 1 and do not exhibit any strong environmental dependence, possibly originating from so-called nature or internal mechanisms. In contrast, for lower galaxy masses and redshifts lower than z~ 1, we observe the emergence in groups of a population of nurture red galaxies: slightly deviating from the trend of the downsizing scenario followed by the global galaxy population, and more so with cosmic time. These galaxies exhibit signatures of group-related secular physical mechanisms directly influencing galaxy evolution. Our analysis implies that these mechanisms begin to significantly influence galaxy evolution after z~ 1, a redshift corresponding to the emergence of structures in which these mechanisms take place.

Aims. The identities of the main processes triggering and quenching star-formation in galaxies remain unclear. A key stage in evolution, however, appears to be represented by post-starburst galaxies. To investigate the prevalence of these galaxies and their impact on galaxy evolution in general, we initiated a multiwavelength study of galaxies with k+aspectral features in the well-studied COSMOS field.

Context. Groups of galaxies are a common environment, bridging the gap between starforming field galaxies and quiescent cluster galaxies. Within groups secular processes could be at play, contributing to the observed strong decrease of star formation with cosmic time in the global galaxy population.